1. Field
The following description relates generally to a thin film transistor and a display device having the same. More particularly, the described technology relates generally to a thin film transistor that can suppress occurrence of a failure due to a crystallization protrusion formed in a semiconductor layer, and a display device having the same.
2. Description of Related Art
Most flat panel display devices, such as an organic light emitting diode (OLED) display, a liquid crystal display (LCD), and the like, include a thin film transistor. Particularly, a low temperature polycrystalline silicon thin film transistor (LTPS TFT) having good carrier mobility can be applicable to a high speed operational circuit and can be used for a CMOS circuit so that the LPTS TFT has been commonly used.
The LTPS TFT includes a polycrystalline silicon film that is formed by crystallizing an amorphous silicon film. A method for crystallizing the amorphous silicon film includes a solid phase crystallization method, an excimer laser crystallization method, and a crystallization method using a metal catalyst.
Among various crystallization methods, a crystallization method using a laser beam has been widely used because it enables low temperature process so that a thermal effect on a substrate is relatively low and enables making of a polycrystalline silicon film having a relatively excellent carrier mobility as high as over 100 cm2/Vs.
However, the crystallization method using a laser beam has a problem in that a crystallization protrusion is formed at the surface of a polycrystalline silicon film crystallized through this method. The crystallization protrusion may deteriorate uniformity of a thin film transistor, that is, the crystallization protrusion has negative influences on the thin film transistor.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.